LCD devices are commonly used as displays for compact electronic apparatuses, because they provide good quality images with little power consumption and are very thin. The liquid crystal material in an LCD device does not emit light. The liquid crystal material must be lit by a light source to clearly and sharply display text and images. Thus, a backlight module is generally needed for an LCD device.
Referring to FIG. 4, a typical LCD device 1 includes a display panel 10 and a backlight module 19 opposite to the display panel 10. The display panel 10 includes a first substrate 11, a second substrate 12 parallel to the first substrate 11, and a liquid crystal layer 13 sandwiched between the first and second substrates 11, 12. A color filter layer 14 is formed on a surface of the first substrate 11 adjacent to the liquid crystal layer 13. Red (R), green (G), and blue (B) filter elements are arranged equidistantly in the color filter layer 13 and separated by a black matrix 15.
The backlight module 19 includes a light source 191, a reflector 192, a light guide plate (LGP) 193, a first diffuser 194, a prism sheet 195, and a second diffuser 196. The reflector 192, the LGP 193, the first diffuser 194, the prism sheet 195, and the second diffuser 196 are positioned in that order, with the second diffuser 196 positioned adjacent to the display panel 10. The light source 191 is positioned adjacent to the LGP 193.
The LGP 193 is used to convert linear light beams emitted by the light source 191 into planar light beams. The first and second diffuser 194, 196 are used to homogenize the planar light beams converted by the LGP 193. The prism sheet 195 is used to convert scattered planar light beams into concentrated planar light beams for promoting a brightness of the planar light beams. The prism sheet 195 includes a base 198 and a plurality of lenses 197. The lenses 197 have the same shape and form a serrated surface on a surface of the base 198 facing the display panel 10.
However, an optical grating is liable to be formed because the lenses 197 are similarly shaped and a distance between each two adjacent lenses 197 is the same. In addition, another optical grating is liable to be formed from the black matrix 15. As a result, Morie fringes are generated as light beams pass through the two optical gratings, thereby deteriorating the display characteristics of the LCD device 1.
Therefore, an improved prism sheet is desired to overcome the above-described deficiencies.